PROJECT SUMMARY/ABSTRACT SYNTHIS SBIR PH I Synthis, LLC is an early stage, New York based biotech company developing a novel immuno-oncology (IO) therapeutic to treat metastatic melanoma patients. The immune checkpoint inhibitors (anti-PD1/-PDL1) are first line therapies for melanoma, but the majority of these patients (?70%) are not responsive, leaving a large unmet need in this cancer population. TGF?? is a pro-tumorigenic cytokine that drives cancer development, in part, by promoting angiogenesis, driving epithelial to mesenchymal transition and suppressing the immune system. General TGF?? antagonists have been developed as cancer therapeutics, but have two serious issues: 1) serious host tissue toxicity due to broad TGF?? receptor expression on normal tissues and 2) potential to increase tumor development due to paradoxical effects on the tumor and surrounding microenvironment. Together, this has led to a small therapeutic window for TGF?? antagonists and limited patient responses. To bypass these negative consequences associated with broad TGF?? inhibition, Synthis has generated a T cell-targeted TGF?? antagonist (T3A) to selectively reverse TGF?? mediated immune suppression and restore mediated tumor clearance. In this Phase SBIR grant, we will determine the efficacy of T3A in combination with anti-PD1 against melanoma tumors in vitro and in vivo. In Specific Aim 1, T3A anti- PD1 will be tested for their ability to restore immune mediated tumor cell killing in the presence of TGF??, with corresponding effector function analysis (i.e., tumor specific T cell expansion). To investigate potential adverse events, the levels of several pro- inflammatory cytokines, such as TNF?? IL1 and IL6, will be measured following treatment. In Specific Aim 2, T3A will be tested in an in vivo human patient derived xenograft (PDX) melanoma model for tumor regression and corresponding intratumoral immune infiltrates. A successful outcome is a 2 fold increase in tumor cell cytotoxicity compared to untreated cells in vitro and a 2-fold increase in tumor infiltrating immune cells or ?35% tumor regression in vivo. These studies validate the feasibility of developing a T3A as an IO therapy and are the prerequisite for pursuing combination in vivo PDX studies with checkpoint inhibitors in Phase II. Virtually every tumor type, including melanoma, has increased TGF?? levels, which correlates with worse prognosis. Advanced melanoma is our first indication since many patients fail immune checkpoint blockade and new options are required to address this unmet need. With nearly 132,000 new melanoma cases annually, the melanoma market is forecasted to be $1.7 billion by 2020 with the immune checkpoint inhibitors accounting for $1.2 billion. T3A will provide new treatment options for melanoma patients in combination with immune checkpoint inhibitors as well as for refractory/relapsed patient populations.